1. Field of the Invention
The present invention relates to an optical recording medium for recording a signal both on a groove and land, and a production method of the same.
2. Description of the Prior Art
For a rewritable high-density optical recording medium, especially a magneto-optical recording medium, a format to realize a capacity as large as 5 to 7 GB on one side (a diameter of 12 cm, i.e., a so called CD size) has been suggested by providing a disc substrate having a thickness of only 0.6 mm, with a numerical aperture NA of 0.6 in an optical system, a single-plate configuration for enabling magnetic field modulation, a recording/reproduction laser wavelength of 630 to 60 nm, a track pitch of 0.6 xcexcm, a recording density of 0.20 xcexcm/bit.
In this case, the groove configuration is a land/groove recording method which is advantageous for a high density.
In the aforementioned land/groove recording method, both of the land and groove are formatted so as to be capable of recording and reproduction and the optical disc has two-spiral configuration of the land and groove.
The land/groove format is an advantageous format for reducing the track pitch. When a tracking signal is fetched with a push-pull signal, it is possible to obtain a signal from two tracks. Accordingly, it is possible to create an error signal up to a half of a conventional track pitch and its polarity is used to identify a land and a track.
Moreover, in reproduction from a magneto-optical recording medium, it is possible to carry out an optical mask based on a difference in the depth of the land and groove. By effectively selecting a depth, it is possible to reduce a cross talk from an adjacent track.
In the aforementioned land/groove recording method also, it is necessary to provide a control signal such as a clock signal for detecting a head of an information signal, and a format for a fine clock has been studied.
In this case, a clock mark is a head detecting signal and should not require a large area.
To cope with this, there has been suggested a technique to provide an address signal and a clock signal by wobbling a groove and to increase efficiency by sharing the clock signal with a data block.
However, this technique has a problem that a jitter is generated in a clock extraction if a recording spot is deviated from the track center.
It is therefore an object of the present invention to provide an optical recording medium capable of providing a control signal in a small area and detecting this control signal such as a clock signal causing little jitter, and a production method of the same.
In order to achieve the aforementioned object, the optical recording medium according to the present invention has a groove and land so that a signal is recorded in both of the groove and the land, wherein each of the groove and the land has a disconnected portion of a predetermined interval so that a control signal is detected from the disconnected portions.
It is preferable that the interval be greater than a diameter of a laser spot for recording and reproducing the optical recording medium.
Moreover, the optical recording medium production method according to the present invention includes steps of: optically cutting a groove by applying a laser beam to a photoresist layer formed on a glass original disc; wobbling the laser beam so as to form a disconnected portion of the groove and a disconnected portion of a land; and producing an optical recording medium original disc by the optical cutting.
The laser beam is two in number, which are wobbled in opposite directions to each other so as to form the disconnected portions.